Threat Vigilance and Intrinsic Amygdala Connectivity

A well documented amygdala-dorsomedial prefrontal circuit is theorized to promote attention to threat (‘threat vigilance’). Prior research has implicated a relationship between individual differences in trait anxiety/vigilance, engagement of this circuitry, and anxiogenic features of the environment (e.g. through threat-of-shock and movie-watching). In the present study, we predicted that—for those scoring high in self-reported anxiety and a behavioral measure of threat vigilance—this circuitry is chronically engaged, even in the absence of anxiogenic stimuli. Our analyses of resting-state fMRI data (N=639) did not, however, provide evidence for such a relationship. Nevertheless, in our planned exploratory analyses, we saw a relationship between threat vigilance behavior (but not self-reported anxiety) and intrinsic amygdala-periaqueductal gray connectivity. Here, we suggest this subcortical circuitry may be chronically engaged in hypervigilant individuals, but that the amygdala-prefrontal circuitry may only be engaged in response to anxiogenic stimuli.

Natural Noise Can Influence Bird Foraging and Vigilance Behavior

Natural sounds are an often overlooked, yet important component of an animal's habitat. The acoustic environment may be especially significant during foraging, because a noisy world can limit auditory surveillance. Here, we investigated how natural noise structures the foraging vigilance trade-off to understand how intense acoustic environments may have shaped antipredator behavior across the evolutionary past, and better inform conservation efforts in the present. First, in Chapter 1, I directly compared the foraging and vigilance behaviors of captive song sparrows (Melospiza melodia) in anthropogenic and natural noise. We recorded foraging trials in 4 playback conditions (roadway traffic, whitewater rivers, whitewater rivers shifted upwards in spectrum, and amplitude-modulated rivers), along with an ambient control to assess which acoustic characteristics make a foraging habitat risky. We found that sparrows increased vigilance or decreased foraging in 4 of 6 behaviors when foraging in higher sound levels, regardless of playback type, indicating a broad role for noise in antipredator behavior. Next, in Chapter 2, I sought to understand the ecological relevance of these findings by examining wild bird behavior. To do so, we broadcast the same whitewater river noise as used in our lab experiment across a riparian landscape. To understand if the spectra of the acoustic environment affected bird behavior, we also presented spectrally-shifted whitewater noise to produce a gradient of frequencies. Using 18 bird feeders placed across this landscape, we recorded and analyzed behavior of the three most common bird species. Black-headed grosbeaks (Pheucticus melanocephalus) and lazuli buntings (Passerina amoena) demonstrated an increase in at least one vigilance behavior in high sound levels, while American goldfinches (Spinus tristis) and grosbeaks altered some behaviors according to background frequency. Clearly, adjusting antipredator behavior in noise is conserved across diverse bird species. Taken together, our findings imply that natural soundscapes have likely shaped behavior long before anthropogenic noise, and that high sound levels negatively affect the foraging vigilance trade-off in both anthropogenic and naturally intense acoustic environments. These results are concerning in light of ever-increasing anthropogenic noise pollution.

A phantom road experiment reveals traffic noise is an invisible source of habitat degradation

Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact.

Vigilance behavior of a tropical bird in response to indirect and direct cues of predation risk

Animals use a variety of cues to evaluate their risk of predation when foraging, including direct cues of predator presence such as vocalizations or scent, and indirect cues, or environmental correlates of predation risk, such as vegetation structure. Research took place in a large-scale forest restoration experiment where habitat patches of different sizes were planted. I examined the effects of predator vocalizations (direct cues) on the vigilance behavior of Cherrie's Tanagers (Ramphocelus costaricensis) foraging in three different locations with varying amounts of vegetation cover (indirect cues): small patches and the centers and edges of large patches. Results show that the indirect cue of predation risk mediated birds' response to the direct cue. The increase in time birds spent alert in response to the predator call was significantly greater in the presumably riskier small patches and large patch edges compared to the relatively safe large patch centers. The increase in frequency of head-turns also was significantly greater in small patches compared to the large patch centers in response to the predator call. Although birds recognized the threat of the predator call and reacted by fleeing more quickly than after the non-predator call, this response did not differ between locations. Birds appeared to integrate information from both types of cues to evaluate their predation risk and determine their vigilance response. Individuals responded more strongly to the direct cue of predation risk when foraging in the presumably riskier smaller patches and large patch edges by increasing vigilance. These results highlight the importance of investigating behavioral responses to the characteristics of forest restoration sites, many of which consist of small patches of habitat.